The typical American diet contains roughly 40-50% fat. These dietary lipids contain predominantly a mixture of saturated and unsaturated fatty acids wi minor components of modified and branched lipids. Dietary lipids function a precursors for membrane phospholipids, are stored in adipose tissue as a fu reserve, are oxidized in the heart and skeletal muscles to meet energy demands and serve as substrates for a variety of enzymes producing bioactiv lipids such as eicosanoids, prostanoids and leukotrienes. High fat diets ar positively correlated in the adult and elderly with the development of obesity and type II diabetes. In addition, clinical data strongly implicate certain lipids, most notably the saturated fatty acids, in the development coronary arterial disease and thrombosis. These observations point out the need for a broader understanding of the basic biochemistry of the structure function and regulation of proteins and enzymes related to the body's utilization of dietary lipids. Dietary fats (triglycerides) are emulsified and hydrolyzed in the gut, packaged by the small intestine and secreted as chylomicron particles. The chylomicra circulate to the tissue beds where the particles are acted upon surface lipases and the liberated fatty acids internalized by target cells. Although a great deal is known concerning the biochemistry of lipoprotein particles and of cellular enzymes involved in lipid biosynthesis/degradatio almost nothing is known about the mechanisms that control the flux of fatty acids into and out of cells. The purpose of this proposal is to examine the structure, function and regulation of the fatty acid transport protein. An analysis of the predicted primary sequence of this protein, along with information gleaned from our laboratory allows us to present the following hypothesis: The fatty acid transport protein facilitates the bidirectional transfer of lipids across the plasma membrane. Moreover, the fatty acid transport protein has an intracellular lipocalin domain which serves as the ligand binding domain and interacts with the cytoplasmic lipid binding proteins. The expression and activity of the transporter is primarily regulated by insulin, thereby controlling the flux of lipids into adipocyte To test this hypothesis we propose to: A: Analyze the activity of the fatty acid transporter, assess the bidirectionality of lipid transport and its regulation by insulin. B. Express the wild-type and mutant forms of the fatty acid transporter to test structure/function relationships. C. Examine the fatty acid binding properties of the lipocalin domain and it interaction with the adipocyte lipid binding protein. D. Analyze the transcriptional control of the fatty acid transporter gene b insulin in adipocytes.